Process and manufacturing equipment for preparing acetals and ketals

ABSTRACT

A process for the preparation of acetals and ketals by reacting an aldehyde or ketone with an alcohol in the presence of an acidic catalyst and removing water by pervaporation. Manufacturing equipment for the preparation of acetals and ketones is also provided.

This application is a divisional of Ser. No. 09/606,918, filed on Jun.29, 2000, now U.S. Pat. No. 6,528,025.

The present invention is concerned with a novel process for preparingacetals and ketals. As is known, acetals and ketals can be prepared byreacting an aldehyde or ketone with an alcohol in the presence of anacidic catalyst. However, the reaction is reversible and, at ambienttemperature or above, the equilibrium of the reaction is shifted to theside of the starting materials, acetal or ketone, and alcohol.

The invention provides a novel process for the continuous preparation ofacetals and ketals in concentrated form and avoids energy-intensivedestination procedures of conventional manufacturing processes, whichare often rendered difficult by the formation of azeotropes.

Thus, the invention is concerned with a process for the preparation ofacetals or ketals which comprises reacting an aldehyde or ketone with analcohol in the presence of solid acid and removing water from thereaction product by pervaporation.

More specifically, the present invention is concerned with a process forrecovering acetals or ketals from reaction mixtures obtained by reactingan aldehyde or ketone with an alcohol, particularly by reaction of alower aliphatic aldehyde or ketone with a lower aliphatic alcohol orsugar alcohol, in the presence of an acid which process comprisessubjecting the reaction mixture containing an acetal or ketal togetherwith water and unreacted aldehyde or ketone and alcohol, to treatmentwith a base followed by pervaporation.

In the following, the term “ketal” and “ketalisation” will be used tosimultaneously denote acetals and acetalisation, respectively. The term“ketone” includes ketones and aldehydes. The term “lower” as used hereindenotes compounds having 1 to 7 carbon atoms. Examples of loweraliphatic ketones are acetone and methyl ethyl ketone. Examples of loweraliphatic aldehydes are formaldehyde, acetaldehyde, propionic aldehyde,butyric aldehyde and isobutyric aldehyde. Examples of alcohols aremethanol and ethanol. Sorbose is an example of a sugar alcohol.

Pervaporation is a known method for separating liquids from mixturesthereof, e.g., for separating water from mixtures with organic liquids,such as alcohols, aldehydes or ketones, see, e.g., European Patent No. 0096 339, and Chem. Eng. Technol. 19 (1996) 117-126. In pervaporationprocesses, the different ability of liquids or gases to permeate polymermembranes is used to separate mixtures thereof.

While pervaporation has been proposed to separate water e.g., fromesterification reactions, the successful application of this method toremove reaction water from acetalisation or ketalisation processes has,so far, not been reported. This is not surprising since in ketalisationreactions the reaction product is in equilibrium with the startingketone and alcohol, and low temperatures are required to shift theequlibrium to the side of the ketal. Pervaporation processes, to becarried out efficaciously, require elevated temperatures where theequilibrium of the ketalisation reaction is shifted markedly to the sideof the starting materials of the reaction.

In a preferred embodiment the process of this invention is carried outin a number of consecutive steps. In a first step, an alcohol is reactedwith an aldehyde or ketone in the presence of a solid acid to obtain anequilibrium mixture comprising the reactants, the desired ketal, andwater. In a second step, the equilibrium mixture obtained is subjectedto treatment with a solid base followed by pervaporation. In a thirdstep the pervaporation retentate is subjected to treatment with a solidacid under conditions that favour ketalisation. In a fourth step, theproduct from the third step treated with a solid base followed bypervaporation. The removal of water from the pervaporation retentate isrepeated until the ketal is obtained in the desired purity which isdetermined by the requirements of the ultimate use of the ketal, i.e. bythe requirements of the reactions wherein the ketal is processedfurther.

The process of this invention can be applied to any ketalisationreaction. Examples of such reactions are

Conversion of acetone to 2,2-dimethoxy propane;

Conversion of methyl ethyl ketone to dimethoxy butane;

Conversion of sorbose to sorbose diacetonide;

Conversion of butendiol to isopropoxy dioxepen;

Conversion of methyl glyoxal to dimal.

In a more preferred aspect, the process of this invention is used toprepare 2,2-dimethoxy propane from acetone and methanol.

In the first step of the reaction in accordance with the invention thesolid acid is suitably a strongly acidic polymer such as a polystyrenesulfonic acid, which may be macroporous or gel-type. Ion exchange resinsconventionally used to catalyze ketalisation reactions can be used.Examples of such ion exchange resins are Dowex 50 (Dow Chemical),Amberlite IR 120, Amberlyst A 15 and A 36 (Rohm & Haas), Lewatit(Bayer). The reaction temperature is suitably from about −50° to about10° C., preferably from about −35° to about −40° C.

Examples of bases as used in the second reaction step are weakly basicion exchange resins such as polystyrenes resins carrying quaternaryammonium groups, e.g. IRA 96 (Rohm & Haas).

For the pervaporation, any membrane which is resistent to the reactionproducts and which are permeable for water may be used. Examples of suchmembranes are hydrophilic membranes which may be polymer or ceramicmembranes. Polymer membranes may be composite membranes comprising asupport layer, e.g. on the basis of acrylonitrile polymers, and apolyvinyl alcohol layer which provides the actual active separatinglayer. Examples of membranes useful in the process of this invention aremembranes provided by Sulzer Chemtech GmbH, D-66540 Neunkirchen, Germanyunder the name Pervap 1055, Pervap 2000 and Pervap 2510; as well asmembranes provided by CM-CELFA Membrantechnik AG, CH-6423 Seewen,Switzerland, under the name CMC-CE-02 and CM-CE-01.

The pervaporation is suitably carried out at elevated temperatures,i.e., temperatures up to the boiling point of the reaction mixture onthe retentate side of the membrane. In general, the pervaporation iscarried out at about 60° to about 130° C. The pressure in thepervaporation is not critical and is basically determined by thepressure required to sustain the mass flow. However elevated pressure,e.g., up to 4 Bar on the retentate side of the membrane can be used,subject to the mechanical resistance of the membrane, to increase theboiling point of the reaction mixture, thus allowing the pervaporationto proceed at higher temperature. The pressure on the permeate side ofthe membran is suitably about 1 to about 500 mBar.

The invention is further illustrated by FIG. 1 which provides a massflow scheme for obtaining substantially pure 2,2-dimethoxy propane fromacetone and methanol, but which may find use for other ketals accordingto the invention.

According to the process in FIG. 1, a mixture of aceton and methanol ina molar ratio of about 2 to about 6 moles, preferably about 4 moles ofacetone to one mole of methanol is cooled and fed into reactor 1 whichcontains an acid ion exchange resin. Reactor 1 is cooled to anappropriate temperature favouring ketal formation, e.g., to atemperature of from about −35 to about −40° C. The flow of the reactionmixture is regulated to allow the reaction mixture to achieve the stateof the equilibrium. Depending on the dimension of the reactor the meanresidence time of the reaction mixture may vary between 1 and 10minutes. The reaction product exiting reactor 1 and containing thedesired product, 2,2-dimethoxy propane, in admixture with water, acetonand methanol is then fed through vessel 2 which contains a basic ionexchange resin into a pervaporation unit 3. Suitably, a heat exchangedevice and a heater is provided between 2 and 3 (not shown in FIG. 1) toallow heat transfer from the aceton/methanol mixture to reaction productexiting 2 and to adjust the temperature required for the pervaporation(about 60 to 70° C.). The permeate from the pervaporation unit 3consists of methanol, water, minor amounts of aceton and traces ofketal. Retentate from the pervaporation unit 3 containing ketal, aceton,methanol and water that was not fully removed in pervaporation unit 3 iscooled to a temperature of from about −35 to about −40° C. and fed intoreactor 4 where it is allowed to achieve the state of equilibrium. Thereaction mixture then proceeds via basic ion exchange resin bed 5,suitably passing a heat exchange device as in the first reaction step,to pervaporation unit 6. The process of adjusting the equilibrium of theretentate at low temperature and submitting the product again topervaporation may be repeated as shown (7, 8, 9). While FIG. 1 showsthree reaction steps it is to be understood that the process of thisinvention is not so limited. Depending on the reaction componentsinvolved and the requirements concerning the purity of the desired ketalone or more reaction steps may be appropriate. In the preparation of2,2-dimethoxy propane, 3 or 4 reaction steps suffice to obtain a productof the desired purity as required for the further use of the product. Aswill be apparent from the above, the ketalisation reaction is carriedout at low temperature whereas the pervaporation is carried out atelevated temperature. Therefore, in a further aspect of the invention,the heat obtained in cooling the reactants in the ketalisation reactionis used to heat up the equilibrium mixture containing the ketal prior topervaporation.

The following Example further illustrates the process of this invention.

EXAMPLE

A mixture consisting of 70 wt % of methanol (factory regenerate;corrsponding to ca. 63 wt % of pure methanol) and 30 wt % of acetone wasfed into reactor 1 of an equipment corresponding to the one shown inFIG. 1 but consisting of four units (one unit=reactor with acid ionexchange resin, vessel with basic ion exchange resin, and pervaporationunit) with a flow rate of 1.0 kg per hour. The reactors with acid ionexchange resin had a volume of a volume of ca. 0.7 L and were chargedwith 530 g of AMBERLYST A 15. The vessels with basic exchange resin hada volume of 0.17 L and were charged with 120 g of AMBERLITE IRA 96. Thereactors and the connecting tubes were made of glass except thepervaporation unit and the tubes leading from the The temperature in thereactors charged with acid ion exchange resin was adjusted to maintainan exit temperature of −34° C. to −36° C. In the pervaporation units themembrane surface was 0.1 m²; the temperature was adjusted to 84° C.; thepressure at the side of the retentate (i.e., before the membrane) was 4bar (abs.), the pressure at the side of the permeate (i.e., behind themembrane) was 30-38 mbar. Membranes of the type CMC-CE-02 (CM-Celfa)were used. The results obtained are given in the Table below:

Reaction Step 1 2 3 4 chem. yield of ketal, 35.8% 42.5% 45.7% 45.9%cumulated chem. yield of ketal per 35.8% 11.6% 5.6% 0.4% step isol.yield of ketal, 35.3% 42.0% 44.9% 44.9% cumulated water content 0.70%0.40% 0.12% 0.10% ketal content 29.54% 43.33% 52.40% 56.92%retentate/feed ratio 70.85% 57.41% 50.80% 46.77% “chem(ical) yield”means % of theoretical (100%) yield “isol(ated) yield” means yield inretentate of individual process step (effective yield that can be used)retentate/feed ratio means retentate obtained in individual process stepbased on mass flow fed into the first reactor

What is claimed is:
 1. A process for the preparation of acetals orketals which comprises reacting an aldehyde or a ketone with an alcoholin the presence of a solid acid catalyst at a temperature from about−50° C. to about 10° C., and removing water from the reaction product bypervaporation at a temperature from about 60° C. to about 130° C. usinga hydrophilic membrane which is polymeric or ceramic.
 2. A process forrecovering acetals or ketals from reaction mixtures obtained by reactingaldehydes or ketones with alcohols in the presence of a solid acidcatalyst at a temperature from about −50° C. to about 10° C., whichprocess comprises subjecting the reaction mixture containing an acetalor a ketal together with water and urireacted aldehyde or ketone andalcohol to treatment with a solid base, being a weakly basic ionexchange resin, followed by pervaporation at a temperature from about60° C. to about 130° C. using a hydrophilic membrane which is polymericor ceramic to remove water from the reaction product.
 3. A process as inclaim 1, wherein the pervaporation retentate is subjected again totreatment with an acid under conditions that favour acetalisation orketalisation, followed by treatment with a solid base, being a weaklybasic ion exchanae resin, and removal of the water from the reactionproduct by pervaporation at a temperature from about 60° C. to about130° C. using a hydrophilic membrane which is polymeric or ceramic.
 4. Aprocess as in claim 3 wherein the treatment of the pervaporationretentate is repeated until substantially pure acetal or ketal isobtained.
 5. A process as in claim 2 further comprising (a) treating thepervaporation retentate with an acid under conditions that favoracetalisation or ketalisation, (b) treating the acetalisation orketalisation product with a weakly basic ion exchange resin, and (c)removing water from the reaction product by pervaporation at atemperature from about 60° C. to about 130° C. with a polymeric orceramic hydrophilic membrane.
 6. A process as in claim 5, furthercomprising repeating steps (a)-(c) until substantially pure acetal orketal is obtained.
 7. A process as in any one of claims 1-4 and 5-6wherein the solid acid catalyst is a strongly acidic polymer.
 8. Aprocess as in claim 7 wherein the strongly acidic polymer is apolystyrene sulfonic acid.
 9. A process as in any one of claims 2-4 and5-6 wherein the weakly basic ion exchange resin used in the treatmentwith the solid base is a polystyrene resin carrying quanternary ammoniumgroups.
 10. A process as in any one of claims 1-4 and 5-6 wherein2,2-di(lower alkyl)-propane is prepared from acetone and a loweralkanol.
 11. A process as in any one of claims 1-4 and 5-6 wherein2,2-dimethoxy-propane is prepared from acetone and methanol.
 12. Aprocess as in any one of claims 1-4 and 5-6 wherein the pressure on theretentate side of the membrane is up to about 4 bar and the pressure onthe permeate side of the membrane is about 1-500 mbar.
 13. A process asin claim 1 or 2 wherein heat produced in cooling the reaction mixture toa temperature from about −50° C. to about 10° C. for the acetalisationor ketalisation reaction is used to heat the reaction product to atemperature from about 60° to about 130° C. in the pervaporation.
 14. Aprocess as in claim 7 wherein the weakly basic ion exchange resin is apolystyrene resin carrying quantemary ammonium groups.
 15. A process asin claim 8 wherein the weakly basic ion exchange resin is a polystyreneresin carrying quanternary ammonium groups.
 16. A process as in claim 7wherein 2,2-di(lower alkyl)-propane is prepared from acetone and a loweralkanol.
 17. A process as in claim 8 wherein 2,2-di(lower alkyl)-propaneis prepared from acetone and a lower alkanol.
 18. A process as in claim9 wherein 2,2-di(lower alkyl)-propane is prepared from acetone and alower alkanol.
 19. A process as in claim 14 wherein 2,2-di(loweralkyl)-propane is prepared from acetone and a lower alkanol.
 20. Aprocess as in claim 15 wherein 2,2-di(lower alkyl)-propane is preparedfrom acetone and a lower alkanol.
 21. A process as in any one of claims1-4 and 5-6 wherein dimethoxybutane is prepared from methyl ethylketone.